This invention relates to a machine for wrapping groups of products in a roll, in particular tissue paper products such as, for example, rolls of toilet paper and/or kitchen paper or products in boxes containing tissue paper products, such as, for example, tissues.
In the packaging of products in a roll—in particular multiple groups of toilet paper or kitchen paper products—wherein the packaging comprises the wrapping of the group of products with a sheet of wrapping material (normally a plastic film), a very highly felt problem is that of obtaining a correct relative positioning of the sheet of wrapping material relative to the product being wrapped before they are inserted as one in the packaging machine.
In effect, this association may be obtained, in the embodiment most commonly used in packaging machines, in a feed station of the machine, which is widely located beneath or alongside an infeed station of the packaging machine, and which has an elevator/conveyor equipped with a loading table which can move alternately towards and away from the machine. The loading table, which is movable between fixed sides, receives the products in a first lowered/withdrawn position and transfers them inside the machine when the relative maximum lifting/transfer position is reached.
During the execution of the feed stroke of the conveyor the products intercept the sheet of wrapping material which has been positioned across the trajectory of the moving products and which is held in a stationary condition by suitable gripping elements.
The above-mentioned operational interaction means that the sheet of wrapping material is:                intercepted by the front end of the product being raised;        disassociated from the gripping elements; and        pulled, lastly, by the product into the packaging machine.        
During this operation the sheet simply rests against the front of the product being transferred; and substantially “swinging” relative to the sides of the product with the free flaps or edges of lateral ends floating substantially freely beyond the lower base of the product.
An example of these stations is known from patent document US 2002/059779 which illustrates a unit for transferring packs of rolls to be packaged in respective films from an intermediate station to subsequent stations. The unit comprises pushing members activated in phase with the positioning of a pack of rolls wrapped laterally by a relative film in the intermediate station. These pushing members intercept laterally the pack of rolls wrapped so as to translate them laterally at the outfeed from the intermediate station.
The release of the sheet, by the gripping elements, and the subsequent pulling of the sheet by the product have always represented critical phases of the feeding, during which the sheet, as it has quite a high a freedom of movement, is susceptible to potential position variations relative to the product to be wrapped. When the sheet does not have printing, wording and/or decorations, any limited variation of the initial positioning may lead to a certain irregularity of the package which, however, if it is not excessive, may generally be tolerated even though it does result in an inherent reduction in the quality of the package.
If, however, the sheet is provided with decorations, wording, printing, that is to say, distinctive signs of the product, even modest variations in positioning and centring of these distinctive signs relative to the product contained inside the package may prove to be completely unacceptable for good or high quality packages.
In addition to this type of known problem there is the fact that, typically for packages having four or more rolls of toilet paper or two or more rolls of kitchen paper, or tissue paper products in boxes, sheets with a thickness of more than 25 um are used, whilst the materials used are typically LDPE (low-density polyethylene) mono-extruded or co-extruded in several layers and then printed with multiple colours.
As mentioned, the presence of printing, like the presence of ionised zones which are more or less uniform joined with the ions which are formed during the first detachment of the layers of superposed film (often configured in feed reels) make the handling of the product sufficiently complex.
Now, however, the requirements of the manufacturers of these types of groups of products are leading towards a reduction in the thickness of the film to achieve an overall saving in the costs of the packages.
These reductions further emphasise the above-mentioned drawbacks:                wrinkling during transport (from the area for unwinding from a roll to the area for raising the product);        possible misalignments (on the sides) of the flaps of the moving film;        slipping caused by the low coefficient of friction which the conveyer belts offer.        
The sum of the drawbacks transforms into:                reduction in the wrapping speed to increase the control of the film;        reduction in quality linked to misalignment defects which result in products rejects at the outfeed to the wrapping machine.        